EXPERIMENTALLY-INDUCED INFECTION WITH BLUETONGUE VIRUS SEROTYPE-11 INCOWS

The consequences of inoculation of bluetongue virus (BTV) serotype 11 into 16 susceptible cows either at the time of breeding or at specifie d stages of pregnancy were studied. The cows were free of BTV or epizo otic hemorrhagic disease virus, and none had antibodies to BTV before virus inoculation. A group of 4 cows was mated naturally to a bull rep orted to shed BTV-22 (CO75B300 strain) in the semen. The bull was susp ected of infecting cows at: mating with BTV-11, which subsequently tra nsplacentally infected the developing fetuses and induced persistently infected and congenitally malformed progeny. Two groups of 4 pregnant cows were inoculated with an insect-derived strain of BTV-11 (CO75B30 0), one group by direct deposit into the uterus at estrus, the other, by intradermal and sc administrations. A 90-day fetus was inoculated i n utero with virus from the same pool. Four pregnant cows were inocula ted with sheep blood-passaged virus of the same BTV-11 strain (CO75B30 0) by intradermal and sc routes. Three cows were inoculated with BTV-f ree suspending fluids and ovine erythrocytes by the intrauterine and i ntradermal-sc routes and were used as in-contact: controls. Infection with insect-derived BTV-11 was confirmed in 3 cows of 1 group by virus isolation and by detection of serum antibodies. The 4 cows inoculated with sheep blood suspension of BTV-11 developed viremia and produced antibodies to the virus. None of the cattle had clinical signs of blue tongue, other than 2 cows that had a slight rectal temperature increas e on postinoculation day 4. All cows and fetuses that ranged in gestat ional age from 69 to 217 days appeared grossly normal at necropsy. Ant ibodies were not detected in fetal blood. Viral antigen was not detect ed in fetal tissues by inoculation into sheep or by immunofluoerscence , and viral RNA was not detected by use of the polymerase chain reacti on. Developmental deformities were not seen in any fetus. The BTV-11 w as not transmitted via the bull semen after natural mating. The BTV-11 strain CO75B300, isolated from this bull and passaged either as insec t-derived or ovine erythrocyte suspensions, infected 8 cows. However, the virus was not transplacentally transmitted to their fetuses. It wa s concluded that there was no evidence for congenital BTV-11 infection in this study.